Water Vapor Transmission Measurement and Significance of Corrections

Water vapor transmission properties of building materials play an important role in the overall moisture management and durability of the exterior building envelopes. The cup method, as described in the ASTM Standard Test Methods for Water Vapor Transmission of Materials (E 96), is widely used in North America and other parts of the world for this purpose. Recently the latest ASTM standard (E 96/E 96M-05) has started taking into account various corrections (e.g., buoyancy correction, correction for resistance due to still air and specimen surface, edge mask correction, etc.) while analyzing the results obtained from the cup methods. This paper presents the results obtained from the laboratory tests carried out on more than 50 building materials. These results have been used to demonstrate the significance of various corrections on the measured water vapor permeability or permeance of various commonly used building materials or components. The results presented in this paper were discussed in the ASTM technical task group to underline the importance of various corrections for the calculation of water vapor transmission properties of various building materials.